Mammography is an x-ray examination of the female breast carried out using medical imaging equipment to obtain mammographic images. Such devices generally have a radiation source for x-rays. The female breast that is to be examined is x-rayed and a radiographic (fluoroscopic) image is obtained on an x-ray film arranged in the beam path below the female breast. During the examination, the female breast is normally held between a compression plate and an object table.
The use of x-ray films has the advantage that it represents a solution that is technically relatively sophisticated and at least in its purchase price relatively inexpensive and at the same time allows the radiographic image obtained by the x-ray film to be archived permanently.
A further advantage of using x-ray films is that x-ray films have a very large receiving surface, typically 18×24 cm or 24×30 cm, and a relatively high spatial resolution of about 14 Lp/mm (Lp=line pairs), which allows a high-definition full x-ray photo of the female breast to be made in a single measurement.
Instead of the x-ray film, which can only be used once, the use of a charge-coupled-device (CCD) sensor is known. The CCD sensors can be used in mammography equipment in the place of the x-ray film.
CCD sensors are electronic components which are suitable for spatial resolution measurement of radiation, in particular, of x-rays and, as a rule, are a matrix of radiation-sensitive cells, also known as pixels. To ensure easy adaptation to existing equipment, the CCD sensor is frequently integrated into a holder in the form of a conventional x-ray film cassette. The advantage of using CCD sensors is that currently available CCD sensors have a resolution of between 10 and 20 Lp per millimeter, which exceeds the resolution of x-ray films and the images are made available immediately and can be processed digitally. Thus, CCD sensors (unlike x-ray films) are suitable for obtaining real-time images (for example, of a biopsy).
The disadvantage of using CCD sensors is that, at present, CCD sensors with the required high resolution have a receiving surface which is markedly smaller than the receiving surface of x-ray films. Therefore, high resolution CCD sensors are currently only suitable for detailed x-ray photos of the female breast.
In addition, within the scope of FFDM (Full-Field Digital Mammography) the use of low resolution digital detectors is known.
The digital detectors used for FFDM currently have a typical resolution of 5 to 10 Lp per millimeter and, hence, a lower resolution than x-ray films. However, it is possible to realize receiving surfaces whose size is similar to the size of the receiving surfaces of conventional x-ray films. Therefore, using FFDM detectors, it is possible to produce a complete image of the female breast in one recording.
Thus, an advantage of the FFDM detectors is that the images are available in real time, the images can be digitally processed, and the receiving surfaces are relatively large. The current disadvantage is the relatively low resolution.
In an alternative to FFDM detectors, the use of digital luminescence radiography with storage screen technology to obtain mammographic images is also known. The resolution that can be achieved using this technology is currently about 8 Lp/mm.
In order to be able to combine the advantages, for example, of an FFDM detector with the advantage of an x-ray film, medical imaging equipment for obtaining mammographic images is known, which equipment has two receiving surfaces for x-rays.
A related art device with two receiving surfaces is shown in FIG. 6. The medical imaging equipment 61 for obtaining mammographic images has a head 62 with a radiation source 63 for emitting x-rays 64 and a receiving device 65.
Both the head 62 and the receiving device are supported by a support column 66, which is, attached to a floor stand or to the ceiling of a room.
In the device shown in FIG. 6, the receiving device 65 has a first receiving surface 71 in the form of a holder for x-ray films and a second receiving surface 72 in the form of a large-area low-resolution detector for FFDM recordings.
The two receiving surfaces 71 and 72 are arranged at right angles to each other and are supported by a support 65 of the receiving device via a mounting 68 attached to the support column 66. The two receiving surfaces 71 and 72 can be pivoted around a rotational axis 70 alternately into a measuring position by turning the support manually. The rotational axis makes an angle of essentially 45° to the beam path of the x-rays 64 emitted by the radiation source 63.
The 45° angle between the rotational axis 70 and the beam path of the x-rays 64, together with the receiving surfaces 71, 72, which are arranged at an angle of 90° with respect to each other, ensures that after the support 65 has been pivoted about the rotational axis 70, one of the receiving surfaces 71 is disposed outside the beam path parallel to the beam path and the other receiving surface 72 is disposed inside the beam path at right angles to the beam path of the x-rays 64.
Provision is made for a measuring region, which is situated in the beam path between a respective receiving surface 71 or 72 in the measuring position and the radiation source 64, the measuring region being provided to arrange an object 67 for measurement.
In addition, a compression plate 75 which is transparent to the measuring radiation is provided in the beam path above the object for measurement 67.
The compression plate 75 is supported by a compression device 74. A vertical movement of the compression plate 75 effected by the compression device 74 enables the object for measurement 67 to be compressed between the compression plate 75 and a supporting surface formed by the respective receiving surface 71 or 72.
The previously known equipment has a disadvantage that it has a high space requirement 73 because of the wide pivoting movement about the axis 70 of the receiving surfaces 71 and 72 held by the support 65.
In addition, the manufacture of a correspondingly pivotable mechanical connection with the respective receiving surfaces 71, 72 having the precision required in the medical sector is technically very complex, and hence expensive.